


Undertale x Sailor Moon: The Crystal Soul

by LolipopPanda



Series: Love of two worlds [1]
Category: Sailor Moon, Undertale, crossover - Fandom
Genre: Cross Over, F/M, Fluff, M/M, Sans is a butt, Smut, Yaoi, intresting twist
Language: English
Status: In-Progress
Published: 2017-07-19
Updated: 2018-11-23
Packaged: 2018-12-04 02:51:08
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 8
Words: 10,340
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11545953
Author URL: https://archiveofourown.org/users/LolipopPanda/pseuds/LolipopPanda
Summary: After having a nightmare of Frisk crying and begging to help them and their friends. Serena goes on the search with the missing small child. With Mina and Luna at her side. Will she and the Sailor scouts be able to save Frisk and the others before another round of cold blooded murders and resets happen once again? And what does this Skeleton name Sans have to do with her Destiny?





	1. The Fallen Princess

**Author's Note:**

> Panda's Note:  
> Eya' all the Sailor Moon and Undertale Fans out there,  
> I wrote this fic because of the dreams I have been having latley along with the photo editing of Sans and Serena.  
> Aka my favorite cross over paring so warning this is a SansxSerenity/ SansxSerena/SansxSailor Moon is the main paring of this fic. As for Darien I did not kill him off because he is still a dear friend to Serena but I did pair him with lovely Fiore himself.  
> Who will also be in the fic later for all of you Darien and Fiore fans out there.  
> Warning: Gore ,Dark, Yaoi, Fluff, Some Bad Words, and Smut.  
> I added the gore and dark part ...Because can you picture what might happen is if Serena's enemies meet Chara?  
> Anyways I hope you all enjoy the fic and thank you so much for trying it out,  
> You are all really amazing.  
> Sincerly,  
> Lolipop Panda

So what if every one had a destiny especially you and so you follow the beginning of that path finding the one who you are supposedly meant to be with.  
Then sometime later your destiny starts to change.  
The one who you loved suddenly isn't the one you are meant to be with anymore. So you now both chose a different path to go on. Sometimes the past life just isn't the future and the present one is and that is exactly how our story is going to begin.  
Where a certain Moon Princess's destiny decides to take a different turn bringing her to a whole new adventure .  
It started off as a normal snowy winter day as a certain group of five girls and two cats one black and one white meet in their usual cafe. For a sudden meeting.  
" Are you kidding me?!" A girl with long raven hair purple eyes shouted having a girl with short blue hair next to her jump slightly while shutting her blue eyes.  
" You didn't have to yell Rei you kinda scared poor Amy out of her studying." A girl with long blond hair tied up into pig tail with a bun at the top of each of them responded in a slight annoyed tone as she narrows her eyes towards her raven haired friend who just rolls hers while taking a sip of her soda.  
" Serena you're just doing this. Because Darien left with Fiore look I totally understand . I mean he was your true love but.."  
"...I'm not doing it because of Darien." Serena said quietly while looking sadly down towards her strawberry shake as she stirs it with her straw.  
" I know its weird but I just don't feel sad at all about Darien and Fiore. Actually I'm happy for them...I mean who knows maybe the destiny of my love life has changed and the person I'm truly meant to be with is still out there...some where." she added with a sweet smile as she looks up from her shake earning a small one back from Rei.  
"There is someone I'm doing this for though."  
"And who is that Serena?"  
"Frisk..."  
" Frisk? You mean Frisk the child who vanished at Mount Ebott?" Amy asked while looking up from her text book with a slight shock look on her face as her pigtail friend gives her a small nod.  
" I've been having nightmares of them crying they were so scare and calling me for help. Asking me to save their friends."  
"But why would Frisk come to you?" a brunette pony tail girl asked with some confusion in her emerald green eyes.  
" ....Well you see Lita I used to baby sit Frisk ever since they were a baby before they had vanished. Their like a younger sibling to me ...and not the more I think about afraid they are the more I need to find them." Serena whispers as tears slowly begin to for in her soft crystal blue eyes.  
"....Serena."  
"Oh come on Rei let her go I'm sure one of us four will be with her."  
" Funny that you mention that." a girl sitting next to their moon princess suddenly added as she jumps into the conversation as if on Que.   
The girl who was sitting next to Serena looked liked she could be her twin only her straight blond hair was a little shorter and pulled half up with a red bow in the back.  
" I'll be with her along with Luna. Artemis will stay here so you three can keep a eye out while we're away. We will have our communicators that can reach from any where to keep in contact with you."   
"...But is Artemis okay with this Mina?" Amy asked as she look towards the white cat who slowly nods his head.  
" As much as I hate Luna going down there with out me. It is good a plan and a way to keep Serena safe and happy." Artemis responded looking towards Luna as she calmly nods her head while sitting on Serena's shoulder.  
"...Fine I can't stop either of you just be careful and keep in communication with us." Rei said with a quiet huff of surrender as she crosses her arms and looks away stubbornly.  
" Thank you Rei."   
" Yeah what ever just be careful Meat Ball head." she responded while giving her klutzy friend a small worried side glance.  
Later that night Mina, Luna and Serena made they way on to the top of mount Ebott finding what seemed like to be some deep hole.  
"...Frisk must of fallen down there." The blond pigtail girl added with her voice shaking from the winter's night cold air blowing on her.  
" There only one way to find out..let's transform before jumping down." Mina ordered earning small head nod from Serena.  
After transforming Sailor Moon gently picks Luna up from the down the ground and walks towards the hole with Venus beside her.  
" It looks like a pretty far drop . You ready for this Sailor Moon?"  
"Ready when you are Sailor V."  
"Alright let's go find Frisk." the yellow sailor scout said as she jumps down the deep whole with her moon princess behind her.


	2. Frisk is Safe

**Summary for the Chapter:**

> Mina and Serena are rescued from a certain evil flower by our favorite goat mama

" Alright so Frisk had to land here but ...their no where in site." Sailor Moon said in a quiet worried tone as she looks around the cavern that they had landed in. With Luna on her shoulder.  
" Which is weird . How can a kid just van...?"  
"Howdy!" a squeaky voice said loudly causing the two girls to turn around finding a small yellow flower monster looking up towards them .   
With an overly friendly expression across it's face.  
" I haven't seen you here before. You two must be new here. Are you looking for Frisk?"  
" How do you know about...?"  
" Careful Sailor Moon there's some thing odd about this weed." Sailor Venus interrupted while blocking her Moon Princess with her gloved arm as she steps in front of Sailor Moon to protect her.  
" Well aren't you a smart little girl? Here have some friendship pallets." Flowey said with a sick laugh as small round objects shoots into Sailor Venus's body causing the the blond protector to fall to the ground in pain.  
" Venus!" Sailor Moon shouted as she kneels beside her friend.  
" Oh don't worry you'll be joining her soo..." the evil yellow flower monster was interrupted as a fireball flies at him causing Flowey to quickly burrow into the ground so the attack wouldn't hit him.  
" Are you alright my child?" A white furred goat woman in a purple dress asked as she rushes over towards them with worry filled in her brown eyes.  
" I-I'm fine but my friend." The princess solider stutters while looking down towards her protector who was now passed out from the pain.  
" Come now we will get to safety. And while I heal your friend perhaps you care to explain why you three are down here. I am Toriel by the way." Toriel said towards Sailor Moon with a sweet smile as she kneels down and lifts Venus into her fury arms.  
" Yes of course..thank you Toriel."  
" You are welcome my child. This way." the kind goat women added as she leads the way towards the sanctuary.  
Once they had reached the ruins Toriel quickly brought the orange sailor scout to a room and begins in healing her as Sailor Moon starts to explain their story to her.  
".. I see so you are protectors then. And the child Frisk does have a family after all ...I had hoped..." The now sad goat woman slowly closed her eyes while letting out a quiet sight as she continues on healing Venus with her magic.  
" Frisk's parents were arrested and sent to prison by the evidence that had shown that there was psychical aggression going on towards them. So if anything I think it would be better if you stay as their adopted mother seeing that you had taken care of Frisk like your own kid after they had fallen." Sailor Moon said with a sweet smile towards Toriel who gave her one it return.  
" Thank you Serena you are to kind....I have a friend who has been watching over Frisk out of the Ruins. He usually comes to visit at this time. I will go down there and talk him into taking you to the child but first a suggestion."  
"Yes?"  
" Please untransform the monsters here are a bit jumpy around humans. So perhaps it will be best if you are in normal clothing instead of armor?"  
" ..I understand . We will normaly clothed when you come back Toriel."  
"Thank you Serena." the kind goat women responded as she leaves the room and walks down the stairs to meet her friend.  
By the time she had finished speaking to her friend and made her way up back towards the bed room.  
Mina and Serena were already in normal clothing and ready to go.  
" I see that you are now fully healed."  
" Yes thank you Toriel I am Mina by the way."  
" You are welcome Mina. Now come my friend said that he will take you to Frisk. He is waiting for you outside." Toriel continues as she leads the way towards the exit with Serena, Mina , and Luna close behind her.  
" Here we are." the white furred goat lady said as she opens the door.  
Revealing a skeleton wearing a blue hoodie, Black basketball short,and pink fuzzy slippers leaning against the tree while typing on his cell phone.  
"Sans I do apologize for the wait."  
" It's fine T..," Sans stops as his white glowing pupils locks with a pair of soft crystal blue eyes.  
They were beautiful he didn't know why but the warmth and kindness in them was putting his soul to ease.  
"..Sans are you alright?"  
" Huh? Heh, sorry about that Tor I have been taking a lot of hours lately . I'm just Bone tired." he finishes with a small wink towards Toriel who lets out a small quiet giggle.  
" Sans this is Mina." The kind goat lady added while placing her paw on Mina's shoulder.  
" And the lovely lady standing in front of you is Serena." she finishes while gesturing towards the owner of the eyes that had sooth his soul.  
Only to have his permanent grin to grow wider.  
Like her eyes Serena's beauty and kindness could make her glow thru any darkness around he couldn't take his eyes off of her.  
" Heh, nice ta' meet ya kiddo." he said while holding out his bony hand.  
" It's nice to meet you to." she responded with a sweet smile while softly taking a hold of his hand with the free hand that wasn't holding Luna and shakes it.  
"Well then ladies are you ready ta' go?" Sans asked with a small with wink towards the pigtail girl who was now blushing softly.  
"See ya' later Tor and don't worry I'll take good care of em'. " the blue hoodie skeleton added with a small wave as he begins to make his way back to Snowdin with the two girls behind him.  
Once they had arrived at the skeleton brother's house in Snowdin.  
The small group found both Frisk and Papyrus busy in trying to solve puzzles in the middle of the living room floor.  
"Ey' kiddo you have a guest." Sans announced .  
Having the small brunette child look up from the puzzle towards the them.  
The look of happiness quickly spreads upon their face as they quickly stood from the sport and rushes towards Serena . Who had already kneel down and open her arm to pull Frisk into a hug once the small child was in front of her.  
A soft sob of relief escaped from her soft pink lips. From finally knowing that Frisk was indeed safe and not dead.


	3. Darkness Meets Serenity

**Summary for the Chapter:**

> Serenity and Chara meets

A few weeks had passed since the two sailor scouts and Luna have fallen into the Underground in hopes of finding Frisk.  
Luckily for them they did including some new friends who had became very close. Over the week Mina had gotten a job at Grillbys while Serena stayed at the Skeleton brother's house keeping in contact with Artemis and the other Sailor scouts.  
" I don't like it . It's to peaceful up here. What if they followed you down there?" Rei's voice asked from Serena's communicator.  
"Gesh Rei you are such a downer." the blond pigtail girl responded in annoyance while shutting her crystal blue eyes.  
" I'm serious Serena ." The raven hair girl voice said in a worried tone.  
"....Look if any alien freaks did follow us . Mina and I will be ready and if we need back up. Luna or one of us will call on you to send someone down. We'll be fine."  
"...Okay look lunch is over I should get to class. I'll tell the others that you are all safe and okay."   
" Thanks Rei see ya." Serena said with a sweet smile as she shuts her communicator.  
A soft knocking sound had Serena slowly turn her head finding Papyrus standing in her door way with Luna in his arms . As Frisk stands beside him with their bangs shadowing their eyes.  
Serena give a small smile to Papyrus as she side glances towards Frisk. With worry in her blue eyes as a dark aura surrounds them.  
" Pigtail human we have finished playing with the adorable cat. Now the small human and I are going outside to practice combat." The tall skeleton announced as a sick smile slowly forms upon Frisk's lips.  
" ....Are you sure should practice this late I mean Sans should be home soon."  
" He usually goes by Grillbys first beside the small human needs to be trained in fighting so . That nothing will happen to them." Papyrus argues while he gently places Luna on the ground having the small black cat runs towards the bed and sits in Serena's lap.  
"... Okay have fun you two." she said with a fake sweet smile.  
Earning a small head nod from Papyrus as he and Frisk leaves the open door way.  
The blond Pigtail girl waited till she heard the front door slam shut from Papyrus's excitement the quickly jumps off the bed and grabs her pink jacket from the closet.  
" Serena what are you doing?" Luna asked with her brown eyes now widen in confusion.  
" I know you sensed the aura on Frisk Luna. Something is wrong....we might have to give our secret away sooner then we plan. That Aura isn't Frisk's it..it was something darker I have to go after them."  
"I can't let you go alone." the black cat said in a worried tone.  
" You have to Luna I need you to get both Sans and Mina . I'll be okay just meet us at the usual place that Papy trains at." Serena said as she rushes out of the room and runs down the stairs while Luna. exits thru the window and runs towards Water Fall after landing on the ground.  
Sans was fast asleep at his hot dog stand only to waken by a female voice.  
"Sans! Sans! Please you must wake up quickly!" The voice said in a panic tone as a small paw pats the top of his head.  
As he slowly opens his eyes sockets Sans finds Luna sitting on the counter in front of him.  
" Uh~"  
" There is no time to explain right now we must go get Mina. And meet Serena in the forest where Papyrus trains. He might be in danger." the black cat interrupted having Sans white glowing pupils vanish from his now pitch black eyes.  
"...Come on...I know a short cut." he said while gently lifting Luna into his arms then walks thru a portal that had formed in front of them.  
Mean while Sailor Moon ran thru the forest as quickly she can finding Papyrus standing in the middle of the clearing with Frisk standing in front of him now holding a sharpen chef knife in their hand with a sick smile on their lips getting ready to attack.  
"No!" she shouted as she runs in front of the tall skeleton only to stop the brunette child from running towards him.  
" Human?! Why did you interrupt mine and the small human's training?! And what are you wearing?!" Papyrus asked now folding his arms across his chest.  
" Because Papy ...That's not Frisk they will hurt you. I'm right aren't I ? You'r not Frisk are you?" the pigtail sailor scout asked as she narrows her blue eyes towards them.  
Only to earn a sick giggle from the child as they lift their head revealing blood red eyes now slightly glowing.  
" Well well aren't you a smart human but. From the armor you are wearing and the soul I see inside you . You are not a normal human. Are you?" Chara asked as they place the back of the knife against their lip.  
"...."  
" Well aren't you being mean not answering my question. Hm~ I have an idea I'll just rip that little mask of your's off. It'll be fun." the possessed child finishes with a lick of their lips while pulling away the blade and holds it in front of them as it begins to glow a bright blood red.  
The small blond pigtail girl let's out a quiet gasp.  
Chara was using her energy to power up their attack. Which made the attack even stronger. Even Sailor Moon wouldn't be able to stop it... there was only one thing that would be able to.  
And she didn't want to use it but if she doesn't Papyrus would be turned into dust and that was something she wasn't going to let happen. The younger skeleton and his older brother have became dear friends to her she didn't want to lose them. Not now not ever.  
"...I have no choice." Sailor Moon whispers as her brooch on her chest begins to glow brightly.  
"Die!" Chara screamed as they slash the air with their knife having the dark red energy fire towards them only to be block by a brilliant flash of light.  
"Paps!" Sans shouted as he walks thru the portal with Mina having the light slightly blinding him.  
His eye sockets widen as the light dies down.  
Revealing a girl in a white long dress with long blond pigtails standing in front of Papyrus holding a silver crystal that seems to be shielding both of them from the possessed child's attacks.  
The small pig tail girl slowly opens her crystal blue eyes towards staring towards Chara with sympathy.  
"...Princess Serenity." Mina whispers having the blue hoodie skeleton look towards her.  
" You three have a lot of explain' ta' do."  
" We will but first Mina turn to Sailor Venus quickly. The princess may need your help." Luna ordered as she jumps on to Sans shoulder while earning a small nod from the long blond haired girl.  
" Venus Power!" Mina shouted while holding a orange stick with a star on top that started glowing brightly as it transforms her into her sailor scout armor then quickly runs towards her moon princess.  
" Princess!" Sailor Venus shouted as she stands next to Serenity.  
"Venus I need you to keep Papy and the others safe . While I free Frisk from the evil spirit that has control of them." the Moon Princess orders earning a small nod from her loyal protector.  
" Be careful princess." Venus whispers as she quickly grabs a hold of Papyrus's hand and pulls him to where his older brother and Luna were waiting for them.  
" Frisk I can sense that your trying to fight them." Serenity said softly as her glowing crystal beam continues fighting the dark energy attack.  
" ...Just hang in there I will get that thing out of you." she finishes while closing her blue eyes. Having the bright beam grow stronger pushing against the dark attack towards Chara who lets out a low growl.  
" It seems like I'm not strong enough...Until next time wanna be princess." the possessed child giggled as they vanished into thin air before the beam could hit them.  
" Oh..Frisk." Serenity whispers as the Silver Crystal returns to its rightful place. Having her turn back into Sailor Moon as she falls backwards from fainting. Only to have to the blue hoodie skeleton quickly teleport behind her and catches the royal sailor scout before she could even hit the frozen ground.  
" That girl." Chara hissed as they lean against a cave wall .  
" Is a nuisance to my plans I have to find a way to get rid of her."  
" Perhaps I can help." An elderly voice said from in front of the possessed child causing them to look up.  
Finding an elderly figure in a robe floating in the air with a crystal ball between their hands as the hood from the robe hid their face.  
" For you see that pest of a princess has something I want . And I cannot have until she is dead." the robe figured chuckles darkly .   
Earning a small smirk from the blood thirsty child.


	4. Serenity Fully Awakens

**Summary for the Chapter:**

> Princess Serenity has fully awakened.

**Notes for the Chapter:**

> Princess Serenity her

After returning to their home Papyrus called both Alphys and Undyne along with Toriel and Asgore to have a meeting at the house. For Luna to explain everything to them.

The four monsters follow closely behind the tall skeleton up the stairs. Towards to what use to be his old bedroom but had. Became both Serena's and Mina's room once they both moved in. Having Papyrus share a room with his older brother.

" Okay, Furball," Sans added as he opens his eyes and looks towards Luna while the five monsters enter the room and shuts the door behind them. 

" Ya' have a lot of explainin' ta' do." he continues while side glancing towards the passed out pigtail girl who was now Serena.

"... A long time ago ...perhaps before the monsters were forced. Into the Underground. There was a beautiful Kingdom on the moon. Ruled by the kind Queen Serenity. The Queen was loved by all in the galaxy including the people and monsters of Earth. For she had protected their home and them with her powers when needed. Serenity had a beautiful daughter....name Princess Serenity. So she had assigned the young princess her guardians. Who would also be her royal court and those protectors were. Sailor Venus Princess of Venus, Sailor Mars Princess of Mars, Sailor Mercury Princess of Mercury, and finally Sailor Jupiter Princess of Jupiter. Together they would protect the young Princess in the Moon Palace. Yet young Serenity was curious about another planet..Earth . There she had met the Prince of that beautiful planet. And they had fallen in love having another woman name Beryl to become jealous. Out of jealousy, she had given her soul to a dark force. That was when she had brainwashed the Earth's people and ordered them to attack the Moon Kingdom. The young Prince was killed in protecting his Princess. Heartbroken Princess Serenity took the Moon sword and use it to end her own life. After the finding, the body of her daughter Queen Serenity was in despair. And yet she knew how to fix this with the last of her strength the Moon Queen used the Silver Crystal to lock the darkness away along with trapping the Princess and the others inside. She then ordered Artemis and I to find the scouts and them while regaining their memories. For she was going to let the crystal break so that they could be reborn on Earth. At the risk of the darkness being freed. So the Princess and others had to be ready to fight. We had sworn to the Queen that it would be done. And so with her final breath, Queen Serenity had used her powers in having her daughter and the others reborn. The last thing Artemis and I had seen was the last tear that ran down our Queen's cheek as she slowly died upon a broken pillar from the Moon Kingdom. After that, we were put into a deep sleep and sent to Earth after the others." Luna finishes as she shuts her eyes while a tear runs down her furry cheek.

" ...Luna, I am sorry...And the Prince?" Toriel asked with a saddened smile.

" He had fallen in love with another. Named Fiore but Serena was fine with it. She said that sometimes we have to find a new path to the future and not follow the old."

" And what about the other protectors?" Asgore asked as he places his paw on Toriel's shoulder while stepping behind her.

"After Frisk had vanished Serena wanted to find her. So the other Sailor Scouts stayed up there to protect the innocents while we came down here." Mina responded with a sweet smile.

"....The Moon Kingdom being destroyed could explain why the monsters were suddenly forced to the Underground." Alphys added while deep in thought.

" Yes, Queen Serenity helped with the peace between the monsters and the humans. After she had passed most likely judgment and fear took over the humankind. And that was when your people were forced Underground." A gentle yet stern voice responded.

Having the Monster and Mina turn towards the owner. Finding a group of three girls standing at the bedroom entrance.

" Setsuna, Lita, Hotaru, you came!" Mina shouted in excitement as she up towards her three friends.

" Of course we came. After you had reported what just had happened. Rei had the three of us come down here." Lita said as Mina pulls her into a tight hug.

"...How is our sweet Princess?" Setsuna asked as she gives Sans a kind smile.

" Heh, still snorin'. For a Princess, the kid can sleep." The blue hoodie skeleton responded with a small wink.

" Well then while Serena rests perhaps we can give you. The tour of the Underground and maybe discuss a few thing in need." Toriel said as she leads the scouts, Luna and the group of monsters out of the room.

" That is a wonderful idea. Female Clone of King Asgore!" Papyrus said as he follows the others out of the room. Only to stop once he realized that his older brother wasn't behind him.

"Sans?! Are you coming?!"

"Nah. I'm gonna keep an eye socket on the kiddo ere'. You go ahead Paps and once ya' are done. Just text me and Serena and I will meet ya' at Grillby's."

",,, Very well brother!" The younger skeleton responded as he exits the room then shuts the door behind him.

An hour later after the group had left. Serena begins to slowly open her crystal blue eyes. Only to find a blue hoodie skeleton fast asleep in the chair next to her bed with his chin resting in the middle of his bony palm.

"... Sans?" the small pigtail girl as she sits up only to have Sans to quickly open his eyes and look down towards her with white pupils now glowing softly.

" Mornin' there Moon Fairy. Did ya' have a nice rest?" he asked with a small wink.

" I-I feel a little better after my nap," she responded with a soft blush only to earn a soft chuckle from the blue hoodie skeleton. 

As he reaches for her long pigtail and gently tugs on it to where her lips were now only a few distance from his permanent grin.

" Heh, I really appreciate you saving my bro an' all but if. Ya' risk like that again I'm am going ta' have ta' punish ya'. Caphice?" he questioned.

Earning a quick nod from a now very red Serena.

" Good little Princess." Sans added while standing up from his seat as he lets go of her soft pigtail.

" I got a text from Paps while you were asleep. He and the others were waitin' for us at Grillby's for a while now." he continues while holding out his bony hand.

With a sweet smile, Serena gently takes a hold of his hand. Only to have Sans quickly pull her towards him. To where she was now leaning against his chest with his arms wrapped around her small waist.

" Hold on tight Serena. We're takin' a shortcut." he whispers softly in her ear.

Causing the short pigtail girl blush softly as she shyly buries her face in the fur of his hoodie.

Before he teleports away with her in his arms.

Once they had arrived Serena gently pulls away from Sans. As she hears her name being called by a familiar voice other than Mina's.

As she looks turns the owner she finds Hotaru waving towards her. With Setsuna, Lita, and Mina standing behind the small child as Toriel and Asgore stood next to them.

" Setsuna, Hotaru, Lita!" Serena giggles as she runs towards them in excitement.

As Sans lets out a low chuckle while following closely behind her.

" I am glad you are well Princess," Hotaru said with a sweet smile as the pigtail girl pulls her into a gentle hug.

"And I'm glad that you are here," Serena responded as she pulls away from the tiny girl.

" Of course when Rei told us that you will be in need of help. We three quickly came in your time of need." Setsuna said with a kinda smile towards her sweet friend.

"....Serena?" Toriel asked quietly having the blond pigtail girl face her with a tilt of her head. As she turns around to face her.

" Asgore and I were talking. And well ...."

" We will like to take you in as our daughter. You will be Princess of the Underground and help protect our people. While the other guardians protect the humans on the surface. And together we will save Frisk. That's if you will welcome our offer of course." Asgore finishes with a small nervous smile.

Only to earn a sweet one from the short pigtail girl.

" I will be honored to." Serena responded while gently taking his paw. Only to glow softly once again.

As the soft light faded around her. She was now standing in front of the king of monsters as Princess Serenity.

" What...How?!" Mina asked in slight shock.

" Her taking back the duties of a Princess. Must have awakened Serenity fully." Luna responded in a happy tone.

" Well, then it would seem that our new friends. Are in good hands." Setsuna added with a sweet smile.

As the other scout's nod in agreement.


	5. The Venus's Flame

**Summary for the Chapter:**

> Mina is jealous of Lita and Grillby

Mina narrows her blue eyes towards the kitchen of Grillby's as she wipes off a drinking glass that she was holding in her hand.

There she could see both Grillby and Lita standing there. Talking to each other the Venus princess could feel a tug of her heart as the flaming monster tells her Brunette ponytail friend some story. Having Lita to let out a soft giggle. 

In her own flirting manner.

This, of course, upsets Mina. Don't get her wrong she was happy that Lita was down there. With them and working with her at Grillby's it was just..she had feelings for the flaming bartender since she had started working there.

And yet she couldn't stop this.

One reason was that she had never seen her fellow sailor scout so happy. And the second...she was the princess of Love. Mina couldn't step in the way of two lovers.

Still, the other half of her wanted to. The jealousy and the wanting of Lita to be happy. Was tearing the poor Venus princess apart any second now she could just rip in half.

" Eya' Blondie you okay there?" A deep voice asked from in front of her.

Causing Mina to look up almost dropping the glass.

As she finds both Sans, Luna, and Serenity sitting in their usual seats at the bar.

"I-I'm fine." Mina stutters as she looks away stubbornly from the three.

" Ya' sure about that?" Sans asked with a raise of his brow bone.

" Y-yes..."

" Mina you know you can tell us. Anything we're your friends." Serenity said with a sweet smile as Luna jumps off of Sans shoulder and sits on the bar between the two.

The Sailor scout was about to lie to them once again. She was going to tell them that nothing was wrong but stops. As she looks towards her sweet Princess's smile. 

With that kinda and caring smile, Mina couldn't lie to Serenity. It was just how it was even when she was still Serena.

It was just who her Moon Princess was. A kind, sweet, and caring friend who was at times a clutz and a crybaby.

".....How do you know that there's something wrong?" The Venus princess asked as she looks back down towards the glass.

" Hate ta' say this kiddo but when. There's something on your mind you become like a certain Moon Fairy we know." The blue hoodie skeleton responded with a low chuckle as Serenity gives him a small playful glare.

Mina couldn't help but smile at the sight of both Sans and Serenity. She didn't know why but the two together was more calming then when Darien was with her pigtail friend.

".... Alright, I'll tell." The blond hair guardian said while setting down the glass that she was a wiping for over twenty minutes.

" It's Grillby."

"What about Grillb's?" Sans asked while placing his chin in the middle of his boney palm.

".... Well, you see...I sorta like him." 

" That's amazing Mina. You should tell him we can hel..."

" That's the thing princess...I think he already knows. For you see Grillby has been avoiding me for a while now." Mina whispers with a sad smile towards her Moon princess.

"....Has he now?" Sans asked as he side glances towards the kitchen where both Lita and Grillby were talking.

"...It's either he knows or he has feelings for Lita." The sailor scout whispers with a hint of sadness in her voice.

That wasn't it. Sans knew if fact that Grillby had strong feelings for Mina. The question why was his old friend avoiding her like some kind of disease. Especially when it's his flamming friend who tells him not to avoid the one who has your soul singing. For it mostly meant that they were meant to be your soulmate.

"...Ey' Kiddo can ya' do me a small favour? And watch over Serenity for a sec I have ta' catch up with an old friend." Sans finishes with a small wink and teleports away before the blond protector could answer.

Only to appear between both Grillby and Lita.

" Eya' pal why don't ya' go hang out with girls for. A bit I have ta' speak with my friend ere' ." The Blue Hoodie Skeleton added with a gesture of his head not even bothering to look towards the Jupiter Princess.

" Yeah sure." Lita said with a sweet smile as she leaves the kitchen.

" Is there something wrong Sans?"

"Yea' you."

" I beg your pardon?"

" Look Grillbs I took your advice. The one that told me not to avoid the one who makes my soul sing. It's one of the main reason I agreed to be er' main protector. Now the question is. Why aren't you takin' your own?" Sans asked while narrowing his eye sockets towards the flaming bartender.

" ...May I ask? What are you talking about or whom?"

"Mina...You're avoiding er' like some disease." 

" She's human Sans."

" Moon Fairy is human should I avoid er' ?"

"No."

" And once again maybe you should take your own advice." Sans growls in annoyance having the flame monster only to stare at him in silence.

"...Look Grillbs all I'm sayin' is that perhaps you should just give in to your feelin's. It might make you a lot happier I mean I am and I'm takin' it one step at a time. Besides I rather see Mina in a Flammin' Relationship with you than any other male monsters out there."

"...Sans."

"You'll be Burnin' up the Underground with talk about how good your two look together." Sans finished with a wink.

Only to have his Flamming friend to let out a small defeated sigh while rubbing his temples.

As much as he hated to admit it Sans was right. He had to tell Mina how he felt about her. Or he will lose her and that was a thing he didn't want to happen.

After their talk, Sans had decided to take Serenity back to the palace. As Grillby let Lita off early for the day since he had planned on closing the bar early.

Before Mina could even start on her last table Grillby gently pulls her to the kitchen to speak with her.

"....Mina during our close there are a few things. I will like to discuss with you."

"...Okay?"

" And then perhaps afterwards...we can have a nice late picnic together. Just you and I." The Flaming bartender added nervously. 

Only to earn a sweet smile from his Venus princess as she gently places a hand on his arm.

" I think I would like that," Mina whispers softly while locking her eyes with his.


	6. Hello Little Princess

**Summary for the Chapter:**

> Sans and Serenity meet Gaster and two surprise guests.

" Wise Man!" Chara shouted as she enters a pitch black room where the hooded man was floating as his hands move over his crystal ball.

" Ah hello to you to Chara I do assume that the black crystal necklace that I have given you. Is keeping little Frisk lock away tightly. Within you?" The wise man asked as he raises his head revealing two glowing eyes from beneath his hood.

" Yes, but that is not the problem at the moment." 

"Oh~? Then if I may ask? What will the problem be?"

" That bitchy moon princess that we're after is now the princess of monsters. And guess who her protector is. Our one and only comedian." Chara finished in an annoyed growl.

" Now now Chara there is no need to worry. For I seem to be a few steps ahead of the dear Moon Princess." the hooded man said with a low chuckle.

As a tall figure behind him slowly vanishes into the darkness that was surrounding the room.

Serenity lets out a small sigh as she shuts her crystal blue eyes while she walks thru Waterfall the small Moon Princess knows that. She should have waited for Sans but Undyne was being overprotective of her.

Yes, Undyne was one of the main protectors of the royal family but even a princess needs some space for herself.

Serenity lets out another soft sigh as she sits in the middle of a field of echo flowers that were softly glowing. The beauty of these flowers is always so hypnotizing to her the princess smiles gently down at the flowers.

It was at times like this Serenity would wonder. If the path that she and Darien had chosed has changed the future. Along with putting the Earth at risk or if Rini was really gone. 

If so it was too late to regret their decision. She will find a way to save Earth if it was heading for a dark path.

The Princess was so deep in thought that she didn't notice the tall figure that was standing behind her. 

" Are you rethinking about your decisions little princess?" A deep voice asked from behind her.

Serenity slowly turns around finding herself face to face with a much taller skeleton monster who seems to be wearing a black coat with dance black pants, wearing white turtleneck beneath the jacket.

She narrows her crystal blue eyes towards the large skeleton monster. There was so much dark energy coming from him. And it was coming from the dark black crystal that was hanging from around his neck.

..Could that crystal be?

"Who are you?"

" Oh my allow me to apologize." He responded with a small bow.

" I am Gaster I once was the head royal scientist of your adopted father King Asgore."

"...Head royal scientist?"

" Yes, and it would seem that our dear ruler has forgotten. Something very important."

"Which is?" Serenity asked not even daring to move the Princess was afraid that if she runs. She would put innocents in danger if this skeleton monster named Gaster would attack during her escape and that cannot happen.

" That human souls can break the barrier and set us free and if what Wise Man had said is true. Yours's my dear which is the crystal soul is more powerful than any of them combine. So I will be taking your soul to free all of us...to free my sons." he mumbles as one of the six hands that were floating around him aims at Serenity preparing to release an attack.

Only to be suddenly shattered by a cyan blue glowing bone.

"...Sans." Gaster whispers having the pigtail princess slowly open her eyes.

Finding her blue hoodie protector now standing between her and the taller skeleton.

" Eya' Gaster it's uh~ been while. Have ta' say didn't think you were the type to betray the royal family. By killin' their daughter." Sans responded with his left eye flaming a cyan blue while is right was pitch black.

" Princess of monsters or not if it is true about her soul she could be the one to set us free. Now Sans hand the human over to me." Gaster finishes while holding out his hand.

" Sorry that ain't gonna happen Gast." the blue hoodie skeleton said with a low growl as one of his Gaster Blasters releases an attack only to be avoided by the taller skeleton.

At first, Serenity was thankful to see him. Then she remembers the black crystal that was hanging around the attacker's neck. Gaster had no control of himself. It was Wise Man controlling him with his twisted lies and Sans was about to hurt an innocent who had a family who was most likely looking for him.

" Sans ..wait."

" Can't do that Moon Fairy," Sans responded while avoiding Gaster's attack and prepared to attack attack again.

" I said wait please." Serenity whispers after standing from the ground and hugging him from behind.

" What are you..? Whoa!" The blue hoodie protector shouted as he teleports away with Serenity to dodge Gaster's blast.

"Are you trying to get us killed?" Sans asked with a quiet hiss as he watches the black coat wearing skeleton float towards them.

"I'm sorry it's just you can't kill him."

" Are you crazy Serenity? Why not? He's trying to get your soul. And uh~ no offense that ain't friendly."

" Because Sans that's not him he's being controlled."

"What?"

I know it's odd to believe but please Sans you have to trust me. I don't want you to kill an innocent and having you only to regret it later." Serenity whispers in a shaky voice while placing her forehead gently against his back.

Usually Sans would argue with this but he couldn't bear to see his princess hurt.

" A'right fine the question now is. How are we going ta' get out of ere' without hurting im'? Sans asked as he narrows his eye sockets towards Gaster who was about to attack.

As if on queue a stream of pink glowing heart and a blue beam of light shoots towards the tall skeleton monster. Causing Gaster to quickly back away before making an angry retreat.

As Princess Serenity blinks in slight shock and confusion.

"..One of those attacks it belongs to..."

" Moon Mama!" A soft voice shouted having both Sans and Serenity turn their head towards a tiny sailor scout with her short pink pigtails bouncing as she runs up to them.

"Chibi Moon? But how..?"

" Chronos and I will explain later. Right now we have to get back to safety where the other scouts are at." Sailor Chibi Moon interrupted with a sweet smile.

" Chronos?" Sans asked with a raise of his brow bone as he looks behind the small sailor scout. Finding a younger male skeleton wearing a nicer version of his hoodie walking towards them.

" What the?"

"As my sis said we'll explain later right now we have ta' get to safety," Chronos said with a small wink.

Earning a small nod from both Sans and Serenity. They would ask for answers first but they both knew that Gaster will return. It seems like that the answers will have to wait for now.


	7. Too Good to be True

**Summary for the Chapter:**

> Sans decides not to give up.

Once the four had arrived inside the living room of the Skeleton brother's house. They all look towards Papyrus who was fast asleep on the couch snoring softly.

" Heh, I guess he fell asleep while waiting for us." Sans chuckles as he makes his way towards his younger brother and lifts him off the couch with his magic.

" You three go ahead and start talkin' I'm going to tuck Paps in and come back down once I'm done." The blue hoodie skeleton added as he makes his way up the stairs with his younger brother floating behind him.

Serenity quietly walks towards the couch and sits on it as she gives both Rini and Chronos a motherly look as they stood across from her.

" Rini, will you care to explain what is going on? For if I am right you should not be existing right now." She said as her future pink hair daughter looks down ashamed.

As Sans suddenly appears next to the older moon princess.

" .....Darien was never really my father... it was a lie to protect the timeline." The tiny sailor scout whispers as she bites her bottom lip.

" A lie?"

"...Yup, the true king of your future kingdom is sitting next to you right now." Chronos added as he tugs on one of his younger sister's pink pigtails to cheer her up.

"Er...What?" Sans asked his eye sockets now pitch black.

" Yup, why so shocked pops? I mean how else how else can mom have a skeleton monster as a son?"

" And how can we trust ya'? I mean come on pal you and this squirt ere' just appeared and now you both are sayin' that your our kids from the future? That's kinda hard ta' believe. Am I right Moon Fairy?" The blue hoodie skeleton asked his princess as he looks towards her who was now giving him a small sweet smile.

" ...Not really." She responded while gently biting her bottom lip.

"... Why, not really?"

"...As I had said earlier when you were tucking Papy into bed. I had thought that Rini no longer exist. She was supposed to be my and Darien's future daughter. We found that out when she came to our time a few years ago. Asking us to help her save her home so thanks to the key Sailor Pluto had given her. We were able to make it to the future. Only to find out that her home was the future Earth and, Moon Kingdom. Along with finding out that she was my future daughter...The question is. Why lie?" Serenity added now looking towards her two children not noticing that her blue hoodie protector had now slightly stiffened.

" That's because dad wanted ta' at least protect some of the future. Ya' know since sis took a certain queen's past self to the future instead of thinkin' what the consequences could be. So~ Pop's asked Edymion to do that one little lie to be on the safe side. At least until it was time to send sis and me down ere' to help out with what's going on along with revealing the truth." the young prince skeleton responded with a small shrug.

"...I can see Sans doing that. What about Darien isn't he still the king of Earth?"

" Nope, after getting together with Fiore uncle Edymion just wanted a peaceful life with im'. So he technically adopted you as his sister making you princess of the Moon and Earth Kingdom. With that you asked him to be dad's advisor. " Chronos finished with a small wink.

"...Sorry ta' interrupt pal but uh~ come on Serenity you can't believe that any of this is true." Sans interrupted having Serenity look towards him with a small worried expression.

"Yes, I do actually."

"Right, you believe that you'll marry a skeleton monster," he said with a small snort.

"Why not?" the older moon princess asked with a small tilt of her head earning a shocked expression from the blue hoodie skeleton.

" Sans, you're sweet, smart, and funny and you don't show it but you have a protective side to where you protect the people you love and care about. And those things along with other things made me fall for you...Sans, I love you." She finishes with a sweet smile only to have him all of the sudden stand up from the couch.

"...Sans?"

" ..I'm.. this is just too good to be....sorry I have ta' go," he mumbles before teleporting away.

Leaving behind a heartbroken Moon Princess.

Seeing the tears filling in his mother's crystal blue eyes. Chronos lets out a small sigh as he makes his way towards the couch with his hands in the front pocket of his hoodie and sits down next to her.

" He loves you too. Just give him some time even dad said he could be very thick Skulled." The young Skeleton prince said with a wink while tapping the side of his skull.

Earning a soft giggle from his mother as his younger sister now in her school uniform comes to sit on the other side of Serenity.

Meanwhile in Waterfall.

San lets out a low groan as he sits at his station. 

He couldn't believe he did that he ran away after the girl of his dreams just told him that she loved him. And yet the story of the future and her telling him that it was just too good to be true he knows a reset could happen anytime and this will all be just some wonderful dream nothing more.

" Sans?" a soft voice called out from in front of him.

Having the blue hoodie skeleton open one eye finding Luna sitting on the table next to his arm.

" Eya' furball."

" I heard what happen while I was sleeping on the kitchen table. Will you like to talk about it?" She asked while placing a paw on his bony hand.

"All of that was just...too good to be true," he mumbles under his breath.

" And why is that?" the royal advisor asked while narrowing her brown eyes.

"....It's cause there's never a happy ending ere'. Many times we were free from the Underground. And the kid would just reset and after that, it would become a Genocide run just for their own sick amusement." He growls now hiding his face in his hands.

" To where I have to watch everyone die again and again," Sans added his voice now shaking with tears.

"... Sans, I do not know if what I am about to tell you will help but I hope that it will. Princess Serenity did not always believe that such a future would become reality. So many times the Earth was under attack so many times did her friends and loved ones have died. Or were put in danger because of the Silver Crystal that is within her. She had started to think that she was weak and nothing but trouble we had try to tell her that it was not true. Yet Serenity did not believe our words. This had all stopped once Rini had come to our time taking us to the future. After seeing this Serenity knew that she could not give up she had to fight for the future she had to believe in herself. And now she had just found out that her future family was not with her ex but with the true one that she truly loves. So the princess will fight for it a lot harder and try her best from keeping a reset from happening. Yet she can not do this alone."

" ....Do ya' think this future could really happen?"

" Well let's look at the facts. Shall we? The two children you have in the future that you say is too good to be true is sitting in your living room right now. So yes I do and in all honesty, I will like this future to happen for I have something to look forward to also ..everyone does." The black cat had finished with a tilt of her head.

To where the blue hoodie skeleton lets out a sigh as he stood from his seat.

" A'right, A'right I know when someone is tellin' me to stop bein' such a lazy bones. ..I guess the time of runnin' and givin' up is over. Thanks, furball." he finishes with a small wink as he vanishes from his station.

Once Sans had arrived in the living room he had found Serenity still sitting on the couch fast asleep with their small daughter who was also asleep using her mother's lap as a pillow.

"There's one. Where's the other?"

"Eya' Pops," Chronos said as he exits the kitchen with a bottle of ketchup in his hand.

" Still up?" the blue hoodie skeleton asked with a raise of his brow bone.

" ... Yup, since you had left I thought that I would watch over Mom and Rini to make sure that they weren't in any danger." The younger blue hoodie skeleton responded with a small shrug of his shoulder as his father now stands in front of him. 

Sans continues staring down at his son. He knew that face it was one he used when he had to lie to Paps. Telling him that he was okay even though he wasn't after one hell of a bad dream about the last timeline before the recent reset.

" Nah, kiddo I think there's more to it a nightmare maybe. You know you can tell your old man anythin'. Right?"

"Oh~ so now you believe that you're my dad after freaking out like that and leaving mom heartbroken? Heh, yeah, some dad." Chronos growls while narrowing his eyes.

"Okay wow, I'm going to ignore that hurtful yet truthful comment since I know for myself that I would be defensive too after a bad dream. You're really are a lot like your old man huh?" Sans asked while rubbing the back of his skull while letting out a soft sigh.

"..."

" Look Chronos, I'm sorry I'm pretty sure that my future self already apologized to you about my reaction earlier. I mean I've been thru a lot of resets and other...nightmares that made me this way. Not believing in a happy ending. But uh~ your sister and you are ere' right now standing right in front of me. Proof that there is one so the past does not give me a good excuse for hurting your mother or you and your sister."

"..."

" I'm just worried about you kiddo. I don't want you to hold it in and go thru what I went thru." the blue hoodie skeleton added now kneeling in front of his son.

"...The Dark Moon kingdom attack." Chronos mumbles under his breath.

" What was that?"

" The attack that happened when sis went to the past. It...got pretty bad. Rini was.. I almost.. but Sailor Moon....I just don't want ta' lose any of you again. " Chronos mumbles under his breath before becoming quiet.

Earning a small sigh from Sans as he places a hand on his sons head.

"A'right, you don't have to say anymore if you don't want ta'. That little and very messy info you had just let out should help at least. Feel a little better?"

"..Yeah, thanks, dad."

" No problem kiddo, now you should get some sleep we have a big day tomorrow. I can't wait to see Tori's face when she finds out that she has grandchildren." the blue hoodie skeleton added with a wink as he stands up.

" So do you want to take Rini upstairs so that you two can sleep in my bed?"

" Nah, we'll stay down ere' the couch was always Rini's favorite place ta' sleep when we stayed with uncle Papyrus." 

" Heh, Paps is going to be excited when you call im' that." Sans added as he makes his way to the couch and kneels in front of his sleeping Moon Princess.

" Hey, Sweet Heart wake up," he whispers in an attempt of not waking his daughter as he sets a bony hand gently on Serenity's cheek.

The older Moon princess slowly opens her blue eyes finding glowing white pupils locked with hers.

"Sans?" Serenity asked with a soft yawn.

" Morin, Beautiful." her blue hoodie protector chuckles quietly as he takes her hand and places a gentle kiss on her open palm having the pigtail princess blush bright red.

" As much as I find our daughter usin' you a pillow adorable. Wanna join me upstairs? So the kiddos can both fit on the couch? "

"J-join you upstairs?"

" Heh, don't worry Moon Fairy I don't plan on doing anythin' to ya," he added while leaning forward to where he was now next to her ear.

" Not with the kiddos and Paps ere' at least. I rather have you all to myself." Sans continues with a small growl before pulling away as Serenity lets out a small shiver.

" Go A Bed and go, mom, I'll watch over Rini," Chronos said with a small wink earning a snort from his father.

" He gets it from you." Serenity added with a small glare towards Sans who give her a small shrug.

" What can I say? Like father like son." the blue hoodie skeleton said as he pulls his Moon princess up from the couch into his arms after Chronos used his magic to levitate Rini so she wouldn't wake up.

" Remember to get some rest kiddo we have a big day tomorrow."

" Sure thing Pops." the young skeleton prince answeres as he sits on the couch and sets his younger sister next to him before shutting his eyes.

Sans stood there for a moment with Serenity making sure that his son was truly asleep before teleporting to his room with the moon princess.

One thing was for sure after finding out that such a future existed he was determined to make that Chara wouldn't ruin it.


	8. Flowery's Second Thoughts

**Summary for the Chapter:**

> The little weed is starting to realize something.

A small yellow flower pops out of the snow in the forested area outside of Snowdin and looks towards the small town from behind one of the many trees.

He was starting to wonder if following Wise man was really a wonderful idea.

After seeing the fight between Serenity and his friend he notices how the moon princess did not attack but concentrated on healing and saving Frisk instead.

Maybe instead of killing the Princess perhaps he and Chara can ask for her help.

The truth was he was getting tired of all these resets as well.

Along with just wanting his body back and helping Chara to have their own instead of Frisk's. He wanted them both to live peacefully with their family and the others.

Instead of killing them. 

The soulless prince knows that he was becoming soft. And shouldn't be but with Frisk giving him mercy at some of the resets he couldn't see himself harming anyone anymore he just wanted his old life back.

"There you are." A voice said with a small giggle having Flowery turn around towards the owner of the voice.

Finding a possessed Frisk standing behind him with their red eyes glowing dimly.

" I was starting to think that you were hiding from me." Chara added now giving him a small glare while taking a step towards him. Having the small flower stiffen in fear.

The truth was he was hiding from Chara.

The way they have been acting lately scared him. Chara would usually let Frisk out at times and allow them to make some choices which at times lead to the Pacifist timelines. But now his dear friend keeps poor Frisk locked in their own body since they were supposedly doing harm to his and Chara's plans.

Even though the monster prince himself were starting to hate those plans now... now he just wanted happiness and peace. And he was starting to get worried about Frisk. The longer they were locked away the more their soul was starting to fade. And he didn't want that to happen yeah he cared but Chara but Frisk was also his friend he just wanted to three of them to be together without either of them dying.

Maybe...perhaps he could talk some sense into Chara if not...then he will have to go with the second plan that he was planning earlier.

 

"...Hey Chara, aren't you getting tired of this I mean of hurting the others and all the resets? Maybe we should stop and let Frisk out again then we can live happily with the others and our new sister all three of us. And maybe Serenity can find a way to give us back lives again." Flowery finishes with a small nervous smile.

" Sorry Asi, but I can't do that." The possessed child responded dryly as the black crystal around their neck begins to slightly glow.

"... I see then Chara forgive me for this." The small yellow flower added with a hurt look while thorned vines wrapped around the demonic child and lifts them into the air as he quickly buries himself into the ground. To escape so that he could find Serenity and asked her and a certain Smiling Trash bag for help.

The young monster prince had always wanted a happy ending and now he is finally going to do the right thing to earn it.

\--------  
Yes I know the Chapter is short but I had to put Flowery in here some how. And trust me I knew this was a perfect ending for the chapter. Don't worry there will be more of our little weed in the story. Who knows maybe he will finally get that happy ending that he had always wanted.


End file.
